This invention relates to novel optically pure borinic esters represented by the formula R*R.sup.1 BOR.sup.2, wherein R* is an aliphatic, alicyclic or heterocyclic chiral moeity, R.sup.1 is an aliphatic, alicyclic, aromatic, heterocyclic or alkynyl achiral moeity, introduced via an organolithium compound, R.sup.1 Li, and R.sup.2 is a simple organyl group such as lower alkyl. The present invention further relates to a process of preparing these optically pure borinic esters and their conversion by reaction with .alpha.,.alpha.-dichloromethylmethylether (DCME) in the presence of lithium tert-butoxide or lithium triethylcarboxide, followed by oxidation with hydrogen peroxide in pH 8 phosphate buffer solution, to optically pure .alpha.-chiral acyclic ketones represented by the formula ##STR1##
Borinic esters are attractive organoborane intermediates in carbon-carbon bond forming reactions. No loss of alkyl groups occur and such 1,2-migrations are known to proceed with complete retention of stereochemistry and configuration of the migratory carbon nucleus. Chiral borinic esters represented by the formula R*R.sup.1 BOR.sup.2 wherein R* is chiral (an optically active organyl group, with boron attached directly to the optically active center) and R.sup.1 is obtained by hydroboration and converted into optically active ketones by reaction of the borinic esters with .alpha.,.alpha.-dichloromethylmethyl ether (DCME) and lithium triethylcarboxide, followed by alkaline hydrogen peroxide oxidation [H. C. Brown, P. K. Jadhav and M. C. Desai, Tetrahedron, 40, 1325 (1984)].
However, alkaline hydrogen peroxide has been observed to cause racemization and epimerization in the conversion of optically active borinic esters to ketones. Also, the borinic esters and therefore the ketones are restricted to groups which are obtainable by hydroboration. Finally, the process is a complex one, requiring a number of steps.
In addition, acyl(1-alkynyl)borinic esters have been prepared in low yield and purity by the reaction of an alkynylboronic ester and Grignard reagent, followed by aqueous acidic workup [D. S. Matteson and K. Peacock, J. Organomet. Chem. 2, 192 (1964)].
The present invention overcomes the disadvantages of the prior art, provides novel achiral and chiral alkyl-(1alkynyl)borinic esters, RB(C.tbd.CR.sup.1)OR.sup.2 and R*B(C.tbd.CR.sup.1)OR.sup.2, and provides a novel process for preparing achiral and chiral ketones employing the novel intermediates.